France's Le Pen Won't Back Either Rival

By

William Horobin and

Gabriele Parussini

Updated May 1, 2012 6:38 p.m. ET

PARIS—French far-right leader Marine Le Pen on Tuesday said she would cast a blank ballot in Sunday's presidential runoff, delivering a stinging rebuke to both President Nicolas Sarkozy and Socialist challenger François Hollande, who have courted her supporters ahead of the vote.

The National Front leader's decision further raises the stakes for Mr. Sarkozy who is fighting for his political survival and seeking to attract the nearly...